Herbicidal compositions comprising the herbicide N-phosphonomethylglycine or derivatives thereof (“glyphosate”) are useful for suppressing the growth of or killing unwanted plants such as grasses, weeds, and the like. Glyphosate typically is applied to the foliage of the target plant. After application the glyphosate is absorbed by the foliar tissue of the plant and translocated throughout the plant. Glyphosate noncompetitively blocks an important biochemical pathway which is common to virtually all plants, but which is absent in animals. Although glyphosate is very effective in killing or controlling the growth of unwanted plants, the uptake (i.e., absorption) of glyphosate by the plant foliar tissue and translocation of glyphosate throughout the plant is relatively slow. Visual symptoms that a plant has been treated with glyphosate may not appear until one week or more after treatment.
Although early visual symptoms of plant treatment generally can be achieved using compositions comprising glyphosate and the contact herbicide pelargonic acid, such compositions have several drawbacks. First, they require high application rates of the pelargonic acid. Second, they often do not permanently kill plants. Pelargonic acid attacks the plant very rapidly so that the glyphosate may have insufficient time to translocate into the plant and completely kill the plant. This drawback is particularly evident when the compositions are used to treat perennial plants such as, but not limited to, Johnsongrass. Third, the compositions are difficult to prepare in a stable formulation; the formulations frequently settle or solidify. Even a tank mix requires essentially constant agitation to prevent the pelargonic acid from separating out. Fourth, pelargonic acid is difficult to formulate in a concentrate, therefore, compositions of glyphosate and pelargonic acid are typically sold in dilute “ready-to-use” formulations.
U.S. Pat. No. 5,196,044 discloses herbicidal compositions comprising, for example, glyphosate that are claimed to reduce the time required for systemic phytotoxic symptoms to appear on the target weed. These herbicidal compositions comprise a first ingredient comprising a fatty acid or mixture of fatty acids such as pelargonic acid, also known as nonanoic acid, (the active ingredient in the contact herbicide SCYTHE®) and a second ingredient selected from a group of herbicides including glyphosate and paraquat. Scythe® has been observed to rapidly burn plant foliage. A too rapid burn may not allow for the complete translocation of glyphosate throughout the plant. As a result, the plant may later recover and continue growing.
Compositions comprising glyphosate are generally formulated with one or more surfactants to enhance their effectiveness for foliar application. When water is added to a composition formulated with surfactants, the resulting sprayable composition more easily and effectively covers the foliage (e.g., the leaves or other photosynthesizing organs) of plants. Glyphosate salts, for example, have been formulated with surfactants such as polyoxyalkylene-type surfactants including, among other surfactants, polyoxyalkylene alkylamines. Commercial formulations of glyphosate herbicide marketed under the trademark ROUNDUP® have been formulated by Monsanto with such a polyoxyalkylene alkylamine, in particular a polyoxyethylene tallowamine, identified as MON 0818. Glyphosate similarly has been formulated with polyoxyalkylene polysiloxane surfactants, in particular polyoxyethylene trisiloxane surfactants, such as the commercial organosilicone surfactant Silwet®L-77, available from Crompton Corporation. Among the numerous studies of the foliar uptake of glyphosate herbicide combined with Silwet® L-77 are those reported by Field & Bishop in Pesticide Science, 1988, Vol. 24, pp. 55–62; Stevens et al. in Pesticide Science, 1991, Vol. 33, pp. 371–82; Gaskin & Stevens in Pesticide Science, 1993, Vol. 38, pp. 185–92; and Gaskin & Stevens in Pesticide Science, 1993, Vol. 38, pp. 193–200. An extensive review of 160 references relating to the use of organosilicones as adjuvants for agrochemicals was provided by Stevens in Pesticide Science, 1993, Vol. 38, pp. 103–22. In fact, so many studies are reported in this area that OSi Specialties has published a Bibliography of Silwet® Organosilicone Surfactants As Agricultural Adjuvants (1996), which is indexed for computer searching. This reference lists hundreds of published studies of commercial organosilicone surfactants in agricultural applications. This bibliography is available to the public through the publisher's office in Tarrytown, N.Y.
WO 98/35561 discloses aqueous herbicidal compositions useful for controlling woody plants when applied to the bark. These compositions comprise glyphosate and a surfactant composition that comprises one or more polyoxyalkylene trisiloxane surfactants and one or more glycols or glycol ethers.
WO 97/23281 discloses surfactant blends comprising organosilicone compounds and a water-soluble surfactant characterized by hydrophobic groups having from about 4 to about 12 atoms. These surfactant blends are useful as spreading agents for the delivery of agriculturally active ingredients such as herbicides.
EP 0 483 095 A2 discloses aqueous compositions comprising glyphosate, the organosilicone SILWET L-77®, and either propylene glycol, dipropylene glycol or polyethylene glycol.
EP 0 531 269 A2 discloses aqueous compositions comprising glyphosate, the organosilicone SILWET L-77®, and an acetylenic diol.
Herbicidal compositions comprising the herbicide dihydrodipyrido(1,2-a:2′,1′-c)pyrazinediium or derivatives thereof (“diquat”) or another bipyridilium, paraquat, also are useful for suppressing the growth of or killing unwanted grasses, weeds, and the like. This contact herbicide typically is applied to the foliage of the target plant and causes rapid disruption of plant cell membranes. It primarily is used as a herbicide to control weeds in noncrop and aquatic areas. Visual symptoms that a plant has been treated with diquat typically appear within 1 to 3 days of application, depending on environmental conditions.
Herbicidal compositions comprising diquat may comprise one or more surfactants. For example, U.S. Pat. No. 5,665,679 discloses compositions containing diquat dibromide and organosilicone surfactants such as Kinetic™, an organosilicone surfactant available from Setre Chemical.
U.S. Pat. Nos. 5,561,099 and 5,658,852 disclose an oil-based agricultural adjuvant comprising an organosilicone compound and a carrier oil. The adjuvant can be used as a spreading agent in combination with herbicides including, but not limited to, glyphosate and diquat.
U.S. Pat. No. 5,504,054 discloses a group of low foaming, superspreading trisiloxane silicone surfactants useful in aqueous spray mixtures comprising herbicides including, but not limited to, glyphosate and diquat.
U.S. Pat. No. 5,558,806 discloses a polyalkyleneoxide polysiloxane surfactant useful as an adjuvant for dispersing, wetting, spreading, and enhancing the efficacy of a herbicide, including, but not limited to, glyphosate and diquat.
U.S. Pat. No. 5,536,700 discloses herbicidal compositions comprising an aryl-5-haloalkylpyrazole and glyphosate, diquat, paraquat or other herbicides.
U.S. Pat. No. 5,532,205 describes herbicidal compositions containing glyphosate, paraquat or diquat, and a photosystem II inhibitor herbicide. The composition is said to provide early burndown symptoms without excessive reduction in regrowth control as compared to a herbicidal composition containing glyphosate and paraquat or diquat. A composition containing glyphosate and diquat or paraquat in a weight ratio of 20:1 is reported to have produced some early burndown symptoms at the cost of long term or regrowth control. A composition containing significantly less diquat or paraquat is said to provide little by way of visible early burndown symptoms.
Chinese Patent Publication No. 1232614 is said to describe a herbicidal composition containing 41% IPA glyphosate salt and paraquat in a ratio of glyphosate salt to paraquat cation of 25:1 to 2.5:1.
It is an object of the present invention to provide novel herbicidal compositions of glyphosate, a bipyridilium (such as diquat or paraquat) and a surfactant that is of a type and present in a concentration sufficient to allow the plant to uptake a herbicidally effective amount of the glyphosate prior to the substantial onset of bipyridilium induced leaf damage that would prevent or severely reduce further uptake of glyphosate by the plant. Use of such novel compositions for the control of unwanted plants provides rapid bipyridilium symptomology (e.g. rapid burndown) yet with the long term control expected of glyphosate based herbicides.
It is a further object of the invention to provide concentrate liquid and particulate solid formulations of glyphosate, a bipyridilium, and suitable surfactant. Such concentrates can be employed to easily prepare the novel herbicidal compositions of the present invention. A still further object of the present invention is to provide a method of controlling or killing unwanted plants by utilizing the novel herbicidal compositions of the present invention.